Model 18 Scope Troubleshooting

[txturbo]

Agreed. Will be interesting to see how bktheking's selector switch is wired since his unit doesn't pop like ours.

By the way, how easily can the FM stereo neon indicator light be replaced? Mine still works but rapidly flickers for a while after start up. I wonder if that is a sign it is failing. When I cleaned my dial glass, I tried to unfasten the stereo indicator to take a closer look but it wouldn't budge. I didn't want to force it for fear of breaking it, so I gave up. Does that orange plastic lens and black lid on the dial side unscrew or just pop off from the rest of the wire assembly behind the dial? And to put a new NE2H lamp in, does it require soldering? Is there a resistor built-in to the stereo indicator wire assembly?

Well... I just put in my new muting LDR. I made it with this photo resistor and lamp from mouser. It works just fine and mutes decently but not 100%. That's how it was new so it's ok by me. I have the 200V jumpered out at the switch. No more pops!

The curent limiting resistors for the neons are on the circuit board, no need to replace them. I don't think you can disassemble the lamp holder, it's molded plastic. You can find a new one without much trouble... Just find one that does not have the current limiting resistor installed.

I removed my indicator when I serviced the receiver. It's just a press fit with a retaining clip. You can unsolder the wires from the board or clip the wire and just repair the connection by soldering the wires, covering it with a bit of shrink tube.

 

[monkboughtlunch]

What's puzzling is why does the selector switch popping not occur on some units (such as bkthekings)? When my selector switch is turned to FM there is a thump. One would think this type of loud pop/thump would not have left the factory and passed quality control inspection with a noise like this present. The original owners of the 18s back in the day surely would have brought this back for warranty service as the massive pop could damage speakers.

Could it be that there is some degraded component somewhere we are overlooking in which the pop issue only crops up after decades of aging? Or is it just degradation of the mechanical selector switch contacts? Or was bktheking's selector switch wired differently?

 

[monkboughtlunch]

Well... I just put in my new muting LDR. I made it with this photo resistor and lamp from mouser. It works just fine and mutes decently but not 100%. That's how it was new so it's ok by me. I have the 200V jumpered out at the switch. No more pops!

The curent limiting resistors for the neons are on the circuit board, no need to replace them. I don't think you can disassemble the lamp holder, it's molded plastic. You can find a new one without much trouble... Just find one that does not have the current limiting resistor installed.

I removed my indicator when I serviced the receiver. It's just a press fit with a retaining clip. You can unsolder the wires from the board or clip the wire and just repair the connection by soldering the wires, covering it with a bit of shrink tube.

Did you use the original LDR metal can? If so, did you have to use a jeweler's saw to open it up?

If it understand you correctly, to change the neon stereo indicator I should take these steps?

1) remove dial glass
2.) pull off the press fit lens covering the neon lamp
3.) unsolder the wire and lamp assembly from the board
4.) use a replacement wire neon lamp assembly (aftermarket), solder to the board. Are there wire / lamp pieces that will fit the original orange lens cover to it can be re-press fit to the new wire/lamp?

 

[txturbo]

That switch has 200v on it to feed the mpx or if board , I forget which one. Carbon tracks , ie dirty selector switch could cause arcing.

Did you use the original LDR metal can? If so, did you have to use a jeweler's saw to open it up?

If it understand you correctly, to change the neon stereo indicator I should take these steps?

1) remove dial glass
2.) pull off the press fit lens covering the neon lamp
3.) unsolder the wire and lamp assembly from the board
4.) use a replacement wire neon lamp assembly (aftermarket), solder to the board. Are there wire / lamp pieces that will fit the original orange lens cover to it can be re-press fit to the new wire/lamp?

I did not use the original can.. I just heat shrinked the parts together.

There is a metal tab on mine that holds it onto the sheet metal. It slides over the back of the lamp.

You can cut the wire and solder onto the old one or, if the wires are long enough you can go to the board.

 

[monkboughtlunch]

Here's a picture of my selector switch (which pops) for comparison with bktheking's (which doesn't pop).

Based on txturbo's post, it looks like if one wanted to jumper the 200V one would need to run a single wire between the two solder points in the lower right where the 3 orange wires terminate.

Question - there is a black wire below with a resistor that appears to run from the power switch to the selector switch. What is the function of that wire and resistor? If that resistor is bad, how does it impact the performance of the selector switch?

 

[txturbo]

Here's a picture of my selector switch (which pops) for comparison with bktheking's (which doesn't pop).

Based on txturbo's post, it looks like if one wanted to jumper the 200V one would need to run a single wire between the two solder points in the lower right where the 3 orange wires terminate.

Question - there is a black wire below with a resistor that appears to run from the power switch to the selector switch. What is the function of that wire and resistor? If that resistor is bad, how does it impact the performance of the selector switch?

Yes.. Just jumper the three orange wires.

No idea about the resistor.

 

[monkboughtlunch]

I wonder if putting a 250v cap, say 22uf or so, in line with the switch would eliminate the pop? Like I said I will open mine, it's a later model iirc, maybe a mod was done by the factory to eliminate the pop.

What points should the 22uf cap be soldered to (see below image)? Would a resistor be need too? Or just use the cap?

 

[monkboughtlunch]

The only reference to popping that the Marantz 18 service manual appears to make is "Low Filter Pops" when the Lo-Filter button is depressed. While that doesn't appear to be the issue here, in addition to adding resistors to the Hi-Lo board, the instructions also make note of replacing two mylar caps on the tone board: C810 and C814. Could replacing the these two caps help filter out the pop arc from the 200V switching? By the way, my unit already has the recommended resistors in the R911 and R912 positions and I am not experiencing popping when the Lo-Filter button is depressed.

 

[txturbo]

What points should the 22uf cap be soldered to (see below image)? Would a resistor be need too? Or just use the cap?

You can try and install a cap but the evidence shows that it won't really do much, if anything. I tried some in line and it made it worse.

Turn your volume down and place the receiver into aux mode to switch the 200V off to the tuner.
Take your volt meter and place the ground lead on the frame.
Take the positive lead and touch it to the 200V line coming from the power supply, the single orange line. Do you hear a small pop? I do on mine.

This means that a >10 meg ohm load causes a pop. Anything you place on the 200V will do it. In fact you can try it on the other power sources and get the same result.

Why does this happen? I am not sure it's worth chasing down....

 

[monkboughtlunch]

I removed my indicator when I serviced the receiver. It's just a press fit with a retaining clip. You can unsolder the wires from the board or clip the wire and just repair the connection by soldering the wires, covering it with a bit of shrink tube.

Would something like these work as a replacement for the stereo indicator neon panel mount indicator since the original appears to be non-relampable? Is there one that fits the original panel mount hole size and has a similar look to the original?

http://www.alliedelec.com/vcc-visual-communications-company-1050c3/70130173/#tab=specs

http://www.alliedelec.com/vcc-visual-communications-company-2150qa3/70130237/#tab=specs

 

[txturbo]

Would something like these work as a replacement for the stereo indicator neon panel mount indicator since the original appears to be non-relampable? Is there one that fits the original panel mount hole size and has a similar look to the original?

http://www.alliedelec.com/vcc-visual-communications-company-1050c3/70130173/#tab=specs

http://www.alliedelec.com/vcc-visual-communications-company-2150qa3/70130237/#tab=specs

Do they have current limiting resistors installed?

 

[monkboughtlunch]

Do they have current limiting resistors installed?

The datasheet suggests that only the green lens version has a resistor: http://www.alliedelec.com/images/products/datasheets/bm/CHICAGO_MINIATURE/70130173.pdf

 

[txturbo]

The datasheet suggests that only the green lens version has a resistor: http://www.alliedelec.com/images/products/datasheets/bm/CHICAGO_MINIATURE/70130173.pdf

You need one without the resistor since it's already on the board.

 

[monkboughtlunch]

Mouser part #511-TIP47
The biggest challenge to replacing the transistors is insulating the 220 package. Just made sure with continuity testing that I was good to go before flipping the switch.

I'm going to order and install the transistors. Do you have a mouser part number for the insulation materials required to insulate the package? Thanks!

 

[monkboughtlunch]

The four scope transistors test fine on my Peak. So far I have left one still installed as the screw does not want to cooperate.I could fight it some more and get it off or just put the originals back in and start looking for other possibly failed components on the board.There has been some heat behind those 3 watt 10K's.View attachment 673969

Do you have an post install photo showing the new transistors in place and how you insulated them? Thanks!

 

[monkboughtlunch]

This means that a >10 meg ohm load causes a pop. Anything you place on the 200V will do it. In fact you can try it on the other power sources and get the same result.

Why does this happen? I am not sure it's worth chasing down....

What are some potential causes for this?

 

[txturbo]

What are some potential causes for this?

Design flaw? Just because it works on one is not a validation that it will work on all.
Bad cap?

As I said, I am not sure that it's worth chasing down any further. Jumpering the 200V kills the pop and the fix could not be simpler.

Before you start replacing your transistors have you tried simply reflowing the solder to them and the scope board? What about the freeze spray test?

Report back some findings

 

[bktheking]

Replace the transistors in the scope circuit, they go bad plain and simple- 90% of the scope failures is a blown one, 10% open winding, $8 and 20 minutes worth of work , easy insurance.

 

[monkboughtlunch]

The January 1969 issue of Popular Science contains an article called "How to Pick the Best Hi-Fi Stereo Compact." The Popular Science panel used the Marantz Model 18 receiver, AR-3A speakers and AR-XA turntable (with V-15) cartridge as the reference system by which they compared test models by other manufacturers. The publication stated "test models fell short of this [Marantz 18] system's performance."

Makes me wonder how good AR-3a's will mate with a Model 18. Anyone heard this combo?

Enjoy!

 

[monkboughtlunch]

page 94: "To get a true picture of where these compacts stand in comparison with the best system you can get--money no object--we set up a reference music system made up of some of the best hi-fi components available. This high-class collection adds up to $1,340 worth -- about $790 more than the highest-priced compact we listened to..."

Using the Inflation Calculator, $1,340 in 1969 would cost a whopping $8,733 today to get an idea of the cost of the Marantz Model 18, AR-XA (Shure V-15) and AR-3A system.